Structural Architecture of Prothrombin in Solution Revealed by Single Molecule Spectroscopy

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biophysics

Background:

• Prothrombin is a key coagulation factor with a complex modular structure.
• Understanding its conformational dynamics is crucial for regulating blood clotting and preventing aberrant activation.

Purpose of the Study:

• To investigate the conformational landscape of prothrombin in solution using advanced biophysical techniques.
• To uncover structural features of functional significance that complement existing crystallographic data.

Main Methods:

• Single-molecule Förster resonance energy transfer (smFRET) to probe conformational dynamics.
• Small-angle X-ray scattering (SAXS) to determine solution structures.
• Analysis of prothrombin wild type and Y93A mutant.

Main Results:

• Prothrombin exists in an equilibrium between open and closed conformations.
• The predominant closed conformation (70%) features an intramolecular collapse, shielding the active site and preventing autoactivation.
• The open conformation (30%) is more susceptible to activation, with SAXS confirming distinct structural envelopes differing by 50 Å.

Conclusions:

• Prothrombin utilizes an intramolecular collapse mechanism in its closed form to prevent premature activation.
• The conformational plasticity and equilibrium between open and closed states provide a new structural framework for understanding prothrombin activation by prothrombinase.